Serial-to-USB don't work at hi-speed

Hello everybody
I’m using a serial-to-USB converter FT4232H Quad HS USB-UART/FIFO IC in order to receive a data stream via /dev/ttyUSB1 (unidirectional, receive only)
I realized that the transmission works fine only up to 115200baud, but at higher baudrates the data are corrupted (even a mere “hello\n” isn’t correctly recognized).

Has anyone information about this issue?

I used the original Angstrom system as well the Debian Wheezy debian-armhf 3.8.13-bone20, with the sane results.
Please note that the same serial connection works fine up to 2Mbit/sec with BeagleBoard-xM

Thanks in advance

Maurizio Cavalli - sw engineer
ControlSystems - Cremona - Italy

Just so people can help, which board is this?


BeagleBone Black Rev.A5C

BeagleBone Black Rev A5C

Some more informations.
It isn’t related to the serial-receiver buffer (Rx FIFO) because also a single character get corrupted.
It isn’t a baudrate mis-agreement, because the transmission BBB->PC works fine, up to 921600.
I tried different values of the ‘ndi_latency_timer’ parameter (default is 1) of the ftdi_sio driver … nothing

First: dismiss Angstron and use Debian
Second: Don’t use tcflush() and discard by yourself the first 8Kb read from the serial line. Maybe the usb-serial driver, the chip itself, or wathever you want, the rx buffer isn’t really cleared.
This way, I can sustain a stream of data packets of 184bytes every millisec, ad 2Mbit/sec.

And last but not least, don’t use the RS signals, but directly the TTL ones